Uniform Work Function Metal Layer for Vertical FET Threshold Control
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Solution Overview
Problem
Conventional vertical field effect transistors (VFETs) face challenges in achieving uniform threshold voltage due to varying thickness of the work function metal layer along the channel region, leading to inconsistent performance characteristics.
Innovation Solution
The implementation of a semiconductor structure with a work function metal layer of uniform thickness along the semiconductor fins, achieved by removing portions of the work function metal layer above the bottom spacer, ensuring consistent thickness and thus uniform threshold voltage across the VFETs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional work function metal layer is deposited over the entire substrate surface including spacers, then the deposition process is simple and complete coverage is achieved, but the work function metal layer thickness varies along the channel region leading to non-uniform threshold voltage
Solution Approach 1:
The work function metal layer is segmented into two distinct portions: a first portion deposited on the semiconductor fin sidewalls and a second portion deposited on the spacer layer. This segmentation allows independent thickness control for each portion, enabling uniform threshold voltage by ensuring consistent metal layer thickness along the channel region while maintaining structural complexity management through defined spatial separation.
Solution Approach 2:
Different regions of the work function metal layer are assigned different functions and thickness requirements. The first portion on the fin sidewalls provides gate control with uniform thickness along the channel, while the second portion on the spacer serves as an extension. This local quality differentiation resolves the contradiction by optimizing threshold voltage uniformity through precise local thickness control rather than uniform thickness everywhere.
2Reliability
If the work function metal layer thickness is made uniform along the channel region, then threshold voltage uniformity is achieved, but the metal layer structure becomes more complex requiring precise thickness control
Solution Approach 1:
The work function metal layer is divided into a first portion on fin sidewalls and a second portion on spacers, allowing independent optimization. The first portion is controlled for uniform thickness to ensure reliable threshold voltage, while the second portion extends the metal layer function. This segmentation achieves performance consistency through controlled uniformity where needed without requiring complex uniformity control across the entire substrate surface.
Solution Approach 2:
The invention applies different quality requirements to different regions: the first portion on fin sidewalls requires precise uniform thickness for reliable threshold voltage control, while the second portion on spacers has different functional requirements. This local quality approach achieves reliability through precise control in critical regions without imposing unnecessary complexity across all regions.
3Manufacturing precision
If portions of the work function metal layer above spacers are removed, then uniform thickness along fins is achieved improving threshold voltage uniformity, but an additional processing step is required
Solution Approach 1:
The invention extracts and removes the excess work function metal layer portion that deposits on the spacer during initial deposition. This extraction step isolates the metal layer on spacers from the critical fin sidewall regions, allowing the remaining first portion on fins to maintain uniform thickness. This taking out approach achieves manufacturing precision for threshold voltage uniformity by eliminating the source of thickness variation, accepting the trade-off of an additional processing step.
Solution Approach 2:
The removal of excess metal layer on spacers is performed as a preliminary action before final device assembly and testing. By addressing the thickness uniformity issue early in the fabrication sequence, the invention prevents threshold voltage non-uniformity from propagating through subsequent processing steps, achieving manufacturing precision while managing fabrication complexity through strategic timing of the removal operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in VFETs with uniform threshold voltage, enhancing performance consistency and reliability by maintaining a consistent thickness of the work function metal layer along the semiconductor fins.
Implementation Method 1
a high dielectric constant layer. A first portion of the high dielectric constant layer is on sidewalls of the semiconductor fin. A second portion of the high dielectric constant layer is over the spacer layer
Implementation Method 2
a work function metal layer on sidewalls of the semiconductor fin. The work function metal layer has uniform thickness
Data Source
AI summary
Provided is a semiconductor structure. In one or more embodiments of the invention, a semiconductor fin on a substrate is provided. A spacer layer is on a surface of the substrate. A high dielectric constant layer is provided, wherein a first portion of the high dielectric constant layer is on sidewalls of the semiconductor fin, and a second portion of the high dielectric constant layer is over the spacer layer. A work function metal layer is on sidewalls of the semiconductor fin, wherein the work function metal layer has a uniform thickness.